Wireless networks have been in use in the public safety sector, e.g., police, fire fighters, emergency workers, etc., for a long time. In the United States, the standard of public safety wireless network is the Association of Public Safety Communications Officials (APCO) Project 25 (P25) Systems whose specifications are the responsibility of the Telecommunications Industry Association (TIA), standard committee TR-8. The P25 standard is an international standard with systems deployed in over 40 counties.
A critical application for public safety wireless networks is group calls in which a member of the group speaks to all other group members simultaneously. The common name for this feature is push-to-talk (PTT). Illustratively, all police officers on patrol may be a part of the same group. When a police officer wants to speak to the group, the police officer “pushes a button” on a handset of the police officer. A message requesting to speak would then be sent from the handset to the public safety wireless network. A floor control mechanism in the public safety wireless network arbitrates all requests to speak in the event that two or more group members attempt to speak at the same time, and the floor control mechanism either grants or denies the request by sending a response back to the police officer.
Public safety wireless networks supporting push-to-talk group calls have coverage areas typically limited to the size of a city area. In addition, different public safety agencies in the same area, e.g., police and fire-fighters, typically operate their own separate networks. Thus, public safety officials traveling to emergency areas outside of their own jurisdiction lose connectivity to their own public safety wireless network. Also, public safety wireless networks supporting push-to-talk group calls utilize older wireless technologies which lack the features and capacity of commercial wireless networks, e.g., wireless networks operated by carriers such as AT&T, Verizon Wireless, Vodafone Group, etc. Furthermore, response times in public safety wireless networks are critical.
Disadvantageously, expanding the coverage areas of existing public safety wireless networks and upgrading public safety wireless networks with technology comparable to that used in commercial wireless networks may be cost prohibitive for the public safety sector. Also disadvantageously, many public safety wireless networks supporting push-to-talk group calls, such as a network of the police department of a small town, have only a limited amount of channels over an air interface. Thus, when a talk group is inactive for some time, the channel used by the talk group must be released for other calls. Further disadvantageously, many public safety wireless networks supporting push-to-talk group calls do not interoperate to allow policemen, firemen or emergency workers to communicate between their respective networks.